(1) Field of the Invention
The present invention relates to an emergency release mechanism for jettisoning an external load supported beneath a helicopter, and in particular to an emergency release mechanism for jettisoning a tree trimming apparatus from a helicopter if the trimming apparatus becomes entangled in trees or other material preventing movement of the helicopter.
(2) Description of the Prior Art
It is known to trim tree limbs and other vegetation alongside power lines using an airborne system comprised of a helicopter having a trimming apparatus suspended beneath the helicopter. Systems used for this purpose are described, for example, in U.S. Pat. Nos. 4,815,263 and 4,984,757. Helicopters are also used to carry other external loads such as cargo, water containers, vehicles, etc., suspended on an attachment member, such as a cable, extending downwardly beneath the helicopter. As used herein, the term “load” is used to generally refer to cargo, trimming apparatus and other objects transported while suspended beneath a helicopter.
One risk in transporting a load beneath a helicopter is that the load can become entangled in vegetation or other objects on the ground, halting movement of the helicopter. Depending on the terrain, the helicopter may be prevented from landing, which can result in the helicopter crashing, causing damage to the helicopter and more importantly, injury or even death to the pilot. Helicopter malfunctions and other emergencies may also result in a need to jettison the load from the helicopter.
To address these concerns, helicopters used to transport external loads commonly include an emergency release mechanism including a quick-release hook that can be actuated by the pilot or co-pilot to separate the attachment member and supported load from the helicopter. For example, U.S. Pat. No. 4,984,757 describes a system comprised of a helicopter having a trimming apparatus attached beneath the helicopter by a release mechanism. A quick-release hook is attached to the bottom of the helicopter chassis. The trimming apparatus boom extends upwardly through a sleeve or tube socket supported on a pivotal frame, known as a trapeze frame, beneath the helicopter with the upper end of the boom being releasably attached to the hook. The hook is actuated by a lever accessible to the pilot. Upon actuation, the hook is opened and the trimming apparatus is jettisoned from the helicopter.
Quick-release hooks used for this purpose are manufactured, for example, by Onboard Systems, Vancouver, Wash. Generally, the hook is comprised of a body and a load beam moveable between open and closed positions to lock around an eye or bar on the cable, boom or other attachment member. The hook includes means to quickly and easily open the hook, such as a hydraulic, electrical or mechanical cable extending from the hook to a release handle adjacent the pilot's seat.
One of the disadvantages of a quick and easy hook release is that the pilot may inadvertently, or even intentionally in a panic situation, actuate the hook release when jettisoning of the load is not in fact required. Considerable cost can result from detaching a load from a helicopter due to lost time, damage to the load, retrieval of the load, and damage to objects struck by the load when it is dropped. Trimming apparatus dropped from a helicopter adjacent power lines can sever power lines or cause tires, resulting in loss of power for considerable periods.
Therefore, there is a need for a load jettisoning mechanism that will provide a secure attachment and allow for a quick release in an emergency, but which will minimize the likelihood of an inadvertent or panic jettisoning of the load when an emergency release is not actually required.